The Characteristics Of Landslides Transformed Into Debris Flows And Numerical Simulation Of Movement Processes In Qin-Ba Mountains

The Qin-Ba mountainous area has an active crust,complex geological structure,variable types of rock and soil structure,well-developed joints and fissures,abundant rainfall,and active human engineering activities.It is a high-risk zone for debris flow disasters throughout the country.In recent years,due to changes in natural conditions,geological disasters in the region have occurred frequently,and they often show the characteristics of sudden,outbreak,transformation of disaster types and chain generation disasters.Landslides and debris flow disasters are often accompanied by landslides.The mudslides in the area have some characteristics of landslides and mudslides.They often scour a huge amount of sand and rocks to the mouth of the ditch in a short period of time,which has a huge impact on the normal production and life of local people.The transformation of landslides into debris flow is a frontier basic issue of the current debris flow discipline.Scholars at home and abroad mostly study unilaterally on the landslide process or debris flow process,and there are few studies on the chain biology of the whole process of landslide transformation to debris flow.Therefore,it is of great significance to clarify the characteristics of the transformation of landslides into debris flows for the prevention and control of geological disasters in the Qin-Ba Mountains.This paper takes the transformation of landslide into debris flow in Qinba mountainous area as the research object.Through relevant data review and field geological environmental investigation,the regional distribution law of landslide transformation into debris flow is summarized and analyzed.On this basis,qualitative analysis and typical examples are carried out on the initiation mechanism of landslide transformation debris flow.The case study obtains the movement characteristics of different types of landslides transforming debris flows;finally,based on the engineering geological conditions of Zhaiziwan Gully debris flow,MatDEM software is used to numerically simulate the process of landslides transforming debris flow.The main results of the thesis are as follows:(1)Two types of landslides transforming debris flows are proposed: breaking and starting landslides transforming debris flows and saturated instability starting landslides transforming debris flows.The former is the accumulation of landslides that have just occurred in the channel to form a landslide dam.Under the influence of hydrodynamic conditions such as heavy rainfall and the nature of the dam itself,it breaks in a short time and initiates the formation of landslides and transforms debris flows;the latter is caused by long periods of time.Under the condition of heavy rainfall over time,the cohesive force and internal friction angle of the slope decrease rapidly,the pore water pressure rises,the slope is close to saturation or directly reaches the saturated state,and gradually decreases to less than the shear stress,and the slope begins to slide along the structural surface.The process of forming a landslide and directly forming a debris flow.(2)Through the analysis of the landslide profile,watershed characteristics,dynamic characteristics,formation conditions and movement process of the landslide transformed debris flow,it can be seen that the Qingshuigou debris flow has experienced the process of landslidemovement-accumulation into dams-failure-debris flow,It is a typical breaking and starting type landslide transforming debris flow;while Zhaiziwangou landslide transforming debris flow does not form a landslide dam.After the landslide occurs,it is directly transformed into debris flow,which is a typical saturated instability start type landslide transforming debris flow.(3)The MatDEM software was used to numerically simulate the transformation process of the Zhaiziwangou landslide into a debris flow,analyze its movement distance map and velocity vector diagram,and reproduce the formation process of the Zhaiziwangou landslide transformed into a debris flow;based on the sequence of the destruction of contact links between active units during the disaster occurrence The sequence sums up the failure modes of the process of landslide transformation into debris flow: shear failure of the slope toe of the upstream slope—tracing fracture of the upstream slope—transformation of landslide into debris flow—integral drainage and erosion of ditch siltation stop;energy conversion in the process of transformation of landslide into debris flow It shows that the reduced gravitational potential energy in the system is finally converted into heat energy,and the friction heat accounts for the highest proportion of the heat energy.(4)The farthest movement distance obtained based on the MatDEM numerical simulation is relatively close to the actual survey results,and the overall average speed obtained is basically consistent with the theoretical estimate,which proves the reliability of the MatDEM software numerical simulation results and the validity of the method.The research methods and results of this paper can provide a theoretical basis for the development and evolution of landslides in the Qin-Ba mountainous area and the prediction of the debris flow range.